Interstitial K+ in human skeletal muscle during and after dynamic graded exercise determined by microdialysis

Interstitial K+ concentrations were measured during one-legged knee-extenso r exercise by use of microdialysis with probes inserted in the vastus later alis muscle of the subjects. K+ in the dialysate was measured either by fla me photometry or a K+-sensitive electrode placed in the perfusion outlet. T he correction for fractional K+ recovery was based on the assumption of ide ntical fractional thallium loss. The interstitial K+ was 4.19 +/- 0.09 mM a t rest and increased to 6.17 +/- 0.19, 7.48 +/- 1.18, and 9.04 +/- 0.74 mM at 10, 30, and 50 W exercise, respectively. The individual probes demonstra ted large variations in interstitial K+, and values >10 mM were obtained. T he observed interstitial K+ was markedly higher than previously found for v enous K+ concentrations at similar work intensities. The present data suppo rt a potential role for interstitial K+ in regulation of blood flow and dev elopment of fatigue.